Procaterol is known as a bronchodilator which stimulates the .beta.-receptor of sympathetic nerves and shows strong bronchodilating activity in very small amounts. The duration of the activity of procaterol is long (8 hours or more), and hence, procaterol is an excellent drug from the viewpoint of duration of time and absorbability.
This drug is generally used in the form of a hydrochloride salt and orally administered in the form of tablets, granules, syrups or administered by inhalation in the form of inhalants or aerosols.
The present inventors have tried to transdermally administer procaterol in the form of conventional cataplasms or tapes in order to externally apply procaterol. However, the present inventors have found that such a preparation for application to the skin has the following disadvantages:
(1) The cataplasms should contain a fixed amount of a drug in a base so that the desired activity of the drug is exhibited. However, since the cataplasms is usually applied in a large amount (1,000 to 1,500 g/m.sup.2), the drug present at the deep portion within the base moves hardly to the surface and is hardly absorbed, and as a result, the availability of the drug is lowered. Therefore, in case of a drug having a strong bronchodilating activity in a very small amount like procaterol, it is not preferable because of remaining of the drug within the base.
(2) On the other hand, when an aqueous base like the base for cataplasms is spread in such a thin layer as 50 to 300 g/m.sup.2, it results in a decreased adhesiveness and an increased evaporation of water, which is not preferable in viewpoint of the properties required for the preparation for application to the skin.
(3) Procaterol can be used in the form of tapes. However, procaterol shows a strong interaction with the base of tapes, which is not preferable in viewpoint of the delivery and availability of the drug.
Under the circumstances, the present inventors have intensively studied for developing an improved preparation for application to the skin suitable for transdermal administration of procaterol. As a result, the present inventors have found that a quite novel preparations for application to the skin can be obtained by incorporating procaterol into a substantially water-free adhesive gel base prepared by dissolving polyacrylic acid in an alcohol and crosslinking polyacrylic acid with a crosslinking agent, and then have completed the present invention. The preparation of the present invention has the following characteristics:
(1) Since the preparation of the present invention contains a larger amount of alcohol in the base than that of conventional tapes or cataplasms, the drug is easily dissolved and dispersedly kept in the base, and hence, there can be prepared a base which allows an excellent drug delivery even when a small amount of the drug is contained in the base;
(2) Polyacrylic acid used in the base inhibits the decomposition of the drug, allowing a stable storage of the drug for a long period of time;
(3) Since the drug dissolved is dispersedly retained within the adhesive gel base, the drug is delivered to the skin at a constant rate, allowing a continuous transdermal absorption;
(4) Since the base contains substantially no water, it is stable and hardly denatured when applied to the skin or during storage; and
(5) The preparation of the present invention has moderate adhesiveness, and hence, can be thinly applied. In addition, the preparation of the present invention does not cause pain when peeled off.